1. Field of the Invention
The present invention relates to a vehicle seat assembly having a hardness gradient and method of making the same. More specifically, the present invention relates to a vehicle seat assembly having areas that are configured to be less hard than other areas of the seat assembly and methods of making the same.
2. Background Art
Generally speaking, a vehicle seat assembly includes three fundamental components: (a) a frame to support the seat assembly and to mount it to a vehicle; (b) a foam cushion to cover the frame; and (c) trim material to cover the foam cushion and provide a durable surface for contact with a vehicle occupant. Typically, the foam cushion is made from an expandable foam material, such as polyurethane, and is molded to a predetermined shape during a molded process. For example, the predetermined shape of a typical bucket-style seat includes raised front, side, and rear bolster areas and recessed central seating and back sections. The trim material may include any number of materials, such as cloth, polymers, or leather. Often, the selection of trim material is governed by the sale price of the vehicle. For example, leather trim material may be used for luxury vehicles while cloth and polymeric materials may be used for less expensive vehicles.
An important consideration in the manufacture of seat cushions is to provide inboard and outboard portions of the seat cushion which are relatively resistant to premature wear while providing an insert or center portion which is soft and comfortable. Inboard and outboard sides of the vehicle seat assembly typically bear most of the load when the occupant gets in and out of the vehicle and therefore require additional rigidity relative to the center insert portion of the vehicle seat assembly. Presently, there is no relatively inexpensive and simple way of providing a vehicle seat assembly having more rigid inboard and/or outboard bolster areas relative to the center insert area.
Accordingly, there is a need to provide a vehicle seat assembly which has a seat cushion that has a relatively rigid outboard and inboard bolster area and a relatively less rigid center portion area which can be manufactured easily and relatively economically.
Moreover, in certain vehicles, occupant sensing systems are provided to help detect whether or not a given seat is occupied and/or the location of and/or the size of the occupant in a given seat. These occupant sensing systems typically include sensors which can be located underneath the foam cushion.
These sensors are typically made of rigid material which can bother the occupant and/or become damaged under the weight of the vehicle cushion. Weight loading from the occupant can press the soft cushion into the relatively rigid sensors. Over time, the cushion and possibly the trim of the vehicle seat assembly can prematurely wear due to repeated loading from the relatively rigid sensors. Once the foam of the seat cushion begins to wear, the occupant is more likely to feel the sensors through the cushion, and this can make sitting on the vehicle seat assembly somewhat uncomfortable.
Accordingly, there is a need to provide a vehicle seat assembly which can accommodate occupant sensing systems without substantial impact on seat comfort to the occupant or damage to the sensor.